Mixing of Triaxial and Intruder Configurations in $^{72,76}$Ge Studied via Multistep Coulomb Excitation

The low-lying states in even-even Ge isotopes have been a subject of intense scrutiny for many years due to the inherent challenge of interpreting their low-energy structure. While several explanations such as vibrational-rotational coupling, 2p-2h intruder mixing and shape coexistence have been proposed, none have been able to satisfactorily reproduce the properties of these low-lying excitations. Recent theoretical calculations have, however, emphasized the importance of the triaxial degree of freedom and, indeed, $^{76}$Ge is proposed to exhibit static triaxiality. In this study, the electromagnetic properties of low-lying states in $^{72,76}$Ge were investigated via sub-barrier multiple Coulomb excitation with GRETINA and CHICO-2. In the case of $^{72}$Ge, the extracted matrix elements seem to agree with the shape coexistence interpretation between the $0_1^+$ and $0_2^+$ states. However, significant mixing between the wavefunctions of these two states and triaxiality are required to reproduce the overall data. These results and calculations based on a triaxial rotor model with configuration mixing will be presented, and the role of triaxiality will be discussed. Preliminary results for $^{76}$Ge will also be highlighted.